1. Field Of The Invention
The present invention relates to a method of manufacturing integrated circuits and other electronic devices. More particularly, the invention relates to an improved process for the etching of silicon nitride on a semiconductor wafer.
2. Description Of The Related Art
Deposited films are used widely in the fabrication of VLSI circuits. These films provide, inter alia, electrical insulation between metals and protection from the environment. One of the materials used in these films is silicon nitride. Silicon nitride is a barrier to sodium diffusion, is nearly impervious to moisture and has a very low oxidation rate.
An etching process is generally used in semiconductor manufacture to transfer resist patterns to circuit features. In particular, etching of silicon nitride is generally accomplished using liquid reagents (e.g., phosphoric acid). This is called a "wet etch." This "wet etch" procedure had inherent problems and limitations given the state of the art for producing VLSI circuits, one of which is related to particulate contamination of the etchant.
One of the problems is that defects are caused by the presence of particulates. This problem is becoming more and more troublesome because of two trends in integrated circuit processing. First, as device dimensions become smaller and smaller, the size of a fatal defect becomes smaller, so that it is necessary to avoid the presence of smaller and smaller particles. Second, there is an increased desire to use large size integrated circuits.
Thus, particulates are not only an increasingly important source of loss in integrated circuit manufacturing yields. Current wet processing steps in integrated circuit manufacture may, therefore, not be viable in the coming years because the liquid reagents generally contain particulates. Contamination of the liquid reagents requires that these chemicals be replaced often, resulting in an expensive waste disposal problem. In addition, many of the liquid reagents used are quite hazardous to human workers process facilities.
Silicon nitride stripping using, for example, phosphoric acid has the problems discussed above. In particular, the process results in particulate and metal contamination which requires future additional cleanup steps. The phosphoric acid used in the stripping process is quite hazardous to human workers and its frequent replacement result in an expensive waste disposal problem.
In addition to the problems of wet etch, there are other etch considerations which must be addressed. It is well known that each material on the substrate exposed to the etch chemistry has a finite each rate. A parameter of considerable importance in pattern transfer is selectivity. Selectivity is defined as the ratio of etch rates between different materials and selectivity with respect to the etch mask has an impact on feature size control. Selectivity with respect to the substrate affects the yield and performance. Therefore, selectivity between the silicon nitride and other exposed materials is a very important consideration when considering any etch process.